Heat sink and mounting arrangement therefor

ABSTRACT

A generally rectangular heat sink is mounted in a conduit box by tabs which are deformed to fit within channels along opposite edges of the heat sink. An access hole in the side of the conduit box and aligned with the channel permits a pin to be inserted therethrough to push the tabs out of the channel and release the heat sink and PC board from the conduit box.

This is a divisional of co-pending application Ser. No. 06/805,965 filedon Dec. 6, 1985.

BACKGROUND AND SUMMARY OF THE INVENTION

With the development of electronic control circuits, and theiradaptation for use with electric motors and the like, there hasdeveloped a need and desire to mount these electronic circuits in closeproximity to the motor. This enhances the utility of the electronics andresults in a more compact design which is also more efficient and lessexpensive to manufacture. However, one significant problem with theassociation of these electronic circuits with an electric motor or thelike is the deleterious effect that heat has on these devices. As iswell known, electric motors can generate a significant amount of heat,and electronic components can be very heat sensitive, especially thosepower transistors or other switching devices which might be used toswitch significant amounts of current to the motor windings.

In the prior art, heat sinks have been developed for the mounting ofthose higher power electronic components requiring heat sinking, butthese heat sinks have generally been attached by merely bolting orscrewing them onto the conduit box or inside the shell of the motor. Ofcourse, the mounting of the heat sink can be critical in that someattention must be paid to dissipating the heat from the heat sink.Generally, this can be done by either exposing the cooling fins of theheat sink to a steady circulation of air or to the exterior of theenclosure, or by bringing the heat sink into close thermal contact witha surrounding enclosure. In some designs, the heat sink is coupled tothe shaft which rotates it as the motor is operated. In other designs,the heat sink is covered but a steady draft of cooling air is blown overthe heat sink. In still other designs, the heat sink is made ofsufficient capacity to operate satisfactorily without exposure toexterior air. However, these designs are susceptible to heat build-upand must of necessity contain greater material and hence be moreexpensive tn those designs exposed to exterior air.

The inventor herein has succeeded in developing two new heat sinkdesigns and mounting for them which represents a dramatic improvementover the prior art in compactness of design, efficiency of operation,and ease in installing and removing the heat sink along with itsassociated electronic circuitry for repair or replacement thereof. Inthe first design, a generally circular PC board is mounted across theopen face of a generally annular heat sink through the electronic leadsof power transistors. As is known in the art, the power transistors arerigidly mounted by their cases to the heat sink and thermally coupledthereto maximize the efficiency of operation of the heat sink, and theelectronic leads from the power transistors are connected by solderingor the like to the PC board itself. By making no other physicalconnections between the PC board and the heat sink, a limited amount offlexure is permitted therebetween. Therefore, with this generallyannular design, the heat sink and PC board is uniquely suited forinsertion within the sleeve of an electric motor or the like bycompressing the heat sink and then releasing it so that it "springs"against the outer shell of the motor sleeve and is held in place throughspring tension. This is achieved by making the arcuate shape of thegenerally annular heat sink somewhat greater than the circular shape ofthe sleeve. Additionally, the heat sink is formed with a plurality ofgrooves or channels extending across the outer face thereof which can befilled with a suitable potting material or fixative to both fix the heatsink against the sleeve and to provide a closer thermal coupling betweenthe heat sink and sleeve so as to improve the heat transfercharacteristics therebetween. This improved coupling and heat transfercharacteristic increases the efficiency of operation of the heat sink.Furthermore, this design permits all of the electronics to be interiorlymounted in the sleeve of the motor which provides a unique compactmounting, eliminating any conduit box. Additionally, removal andreplacement or repair of the electronic circuitry is easily achieved bydisconnecting a few wires, releasing the potting compound with anappropriate method as is known in the art, and removing the heat sinkand associated PC board by compressing the heat sink and withdrawing itaxially from the motor sleeve. Thus, this heat sink design combines allof the desired characteristics for a heat sink including efficiency ofoperation, compactness of design, and ease in installation and removal.Furthermore, the heat sink can be constructed of extruded aluminum suchthat it is easily and cheaply manufactured.

For those motor designs which include a conduit box, the inventor hassucceeded in developing a unique mounting arrangement which is not onlyinexpensive and easily manufacturable, but which also maximizes theoperation of the heat sink by exposing the cooling fins to the exteriorair. Still another advantage of this heat sink and its mounting is thatit is simply and easily installed by deforming tabs cut into the sidewall of the conduit box into channels integrally formed in oppositesides of the heat sink. An access hole to each channel permits theinsertion of a pin through the channel which forces the tabs back intotheir preassembled configuration for removal of the heat sink and PCboard for repair or replacement. Not only is removal easilyaccomplished, bu the tabs are reusable for replacement of the heat sinkand PC board. With integrally formed tabs in the side wall of theconduit box, there is no hardware to be lost or misplaced and additionaltabs can easily be cut or punched in the conduit side wall should theoriginal tabs break off. This heat sink design combines many of the samefunctional advantages and features in a somewhat different structuralarrangement from the first design as it is for use with a conduit box.These functional features include optimal efficiency for exposingcooling fins to exterior air, ease in installation and removal, withrepeated removal being possible with the same structure, the eliminationof mounting hardware, compact design, and maximum utilization ofavailable space.

Some of the principal advantages and features of the invention have beensummarized for convenience above. A fuller understanding of theinvention, and a complete description thereof is contained in thedrawings and description of a preferred embodiment which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of an electrical motor with the annular heat sinkcontained therein;

FIG. 2 is a partial cross sectional view of the annular heat sinkcontained within the motor sleeve;

FIG. 3 is a cross sectional view taken along the plane of line 3--3 inFIG. 2 and detailing the PC board as mounted to the annular heat sink;

FIG. 4 is a cross sectional view taken along the plane of line 4--4 inFIG. 2 and detailing the mounting of the annular heat sink within themotor sleeve;

FIG. 5 is a partial view taken along the plane of line 5--5 in FIG. 4detailing the mounting of the power transistor to the heat sink;

FIG. 6 is a partial perspective of the annular heat sink detailing thechannels formed therein;

FIG. 7 is a perspective view of the second embodiment of the heat sinkfor use and mounting in a conduit box;

FIG. 8 is a partial cross sectional view taken along the plane of line8--8 in FIG. 7 and detailing the channel mounting;

FIG. 9 is a partial cross sectional view taken along the plane of line9--9 in FIG. 8 and broken away to detail the mounting of the powertransistors to the heat sink;

FIG. 10 is a partial cross sectional view taken along the plane of line10--10 in FIG. 8 further detailing the mounting of the power transistorsto the heat sink; and

FIG. 11 is a partial cross sectional view detailing the insertion of thepin through the channel to release the heat sink and PC board from itsmounting.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in FIG. 1, an electric motor 20 or the like generally has acylindrical sleeve 22 surrounding and enclosing it, with an output shaft24 extending along the central axis thereof. This cylindrical sleeve 22can be extended in length to provide a convenient location for mountinga PC board 26 and an associated heat sink 28 within the sleeve 22 so asto maintain the overall cylindrical shape of the motor 20. As best shownin FIGS. 2-4, the PC board 26 is generally a circular flat disk with aplurality of components 30 mounted thereon and soldered thereto, asknown in the art. Also mounted to the PC board 26 are up to six powertransistors 32 with their leads 34 extending through the PC board 26,and with a screw 36 extending through the case 38 thereof to mount it tothe generally annular heat sink 28. Thus, the power leads 34 oftransistors 32 provide the only mechanical connection between the PCboard 26 and the heat sink 28. With this construction, a limited amountof radial flexure is permitted between the heat sink 28 and PC board 26.

As best shown in FIG. 6, a plurality of channels 40, 42 of varyingdimension are formed along the outer surface of the heat sink 28. Thesechannels 40, 42 provide a convenient structure to grasp the heat sink 28and compress it for insertion or removal from the sleeve 22, and alsoprovide a reservoir for a potting compound, such as RTV, which serves tofix the annular heat sink 28 in position and improve the thermalcoupling between heat sink 28 and sleeve 22. As is best shown in FIG. 4,the annular heat sink 28 extends around virtually the entirecircumference of PC board 26 to thereby maximize the thermal couplingbetween the heat sink 28 and sleeve 22. Of course, the heat sink 28 canbe made wider, but this would require a longer sleeve 22.

A second embodiment is shown in FIGS. 7-11. In this embodiment, aconduit box 44 is secured around the periphery of shell 22, and heatsink 46 is generally rectangular shaped an includes a plurality ofcooling fins 48 along the back surface thereof. As in the firstembodiment, a PC board 50 containing various electronic components 51 isconnected to the heat sink 46 by a plurality of power transistors 52with screws 53 extending through the case or mounting tab 54, and theelectrical power leads 56 soldered directly to the PC board 50.

In this embodiment, the PC boad 50 and heat sink 46 is secured to theconduit box 44 by one or more tabs 58 which are cut or stamped into theside wall of conduit box 44. These tabs 58 are deformed into a channel60 formed along either edge of heat sink 46 to thereby mount the PCboard 50 and heat sink 46, as best shown in FIGS. 8 and 11. These tabs58 (in conduit box 44) are generally formed by this sheet metal and areintegral with the conduit box 44. Heat sink 46 may be made of extrudedaluminum, roll formed aluminum stock, or other similar material, asknown in the art, and channels 60 can be integrally formed therein.

As shown in FIGS. 7 and 11, removal of heat sink 46 and PC board 50 iseasily achieved through insertion of a pin 62 or the like through anaccess hole 64 in conduit box 44. Insertion of the pin 62 along thechannel 60 forces the deformed tabs 58 to return to substantially theiroriginal location which permits the PC board 50 and heat sink 46 to beeasily removed from the conduit box 44. Thus, this embodiment optimizesthe cooling efficiency of heat sink 46 by exposing the cooling fins 48to the exterior air, and also provides quick and easy installation andremoval with no hardware.

There are various changes and modifications which may be made to theinvention as would be apparent to those skilled in the art. However,these changes or modifications are included in the teaching of thedisclosure, and it is intended that the invention be limited only by thescope of the claims appended hereto.

What is claimed is:
 1. In a dynamoelectric machine having a conduit boxand an associated electronic circuit mounted on a PC board, theimprovement comprising means to mount said PC board to the conduit box,said mounting means comprising means defining a channel along at leastone edge of the PC board, and means defining at least one tab in theconduit box so that said PC board may be releasably mounted therein bydeforming the tab into the channel.
 2. The device of claim 1 furthercomprising means to access said tab and channel after the PC board ismounted in the conduit box so that the tab may be returned substantiallyto its first location to release the PC board from the conduit box. 3.The device of claim 2 wherein the access means comprises means defininga hole aligned with the channel.
 4. The device of claim 3, wherein thetab is integral with the conduit box at an edge nearest the access holeso that a pin driven through the access hole and channel bends the tababout its integral edge and out of the channel to release the PC board.5. The device of claim 4 further comprising a heat sink mounted to thePC board, the channel being defined in the edge of the heat sink.
 6. Thedevice of claim 5 wherein at least two tabs are formed in the conduitbox, said tabs being aligned with the channel.
 7. The device of claim 5wherein at least two tabs are formed along opposite sides of the conduitbox, and wherein the heat sink has a channel on opposite sides thereofso that the heat sink and PC board are mounted by two tabs deformed intoeach of two channels on opposite sides thereof.
 8. In a dynamoelectricmachine having a conduit box and an associated electronic circuit with aheat sink mounted thereto, the improvement comprising means toreleasably mount the PC board and heat sink to the conduit boxcomprising at least one tab cut into the side of the conduit box, andmeans defining a channel along at least one edge of the heat sink sothat deforming the tab into the channel secures the PC board and heatsink to the conduit box.
 9. The device of claim 8 further comprisingmeans defining a hole in the conduit box and aligned with the channel sothat insertion of a pin through the hole and into the channel forces thetabs out of the channel to release the PC board and heat sink from theconduit box.
 10. The device of claim 9 wherein two tabs are formed ineach of two opposite sides of the conduit box, and a channel is formedin each of two opposite sides of the heat sink.
 11. The device of claim10 wherein the heat sink has cooling fins formed along a surfacethereof, and wherein the mounting means includes means to orient saidcooling fins outwardly from the conduit box.